Method for the preparation of feed pellets

ABSTRACT

The present invention discloses a method for obtaining feed pellets. The method comprises the addition of active ingredients to feed pellets after the pellets have been extruded. The method further comprises the addition of a solution or suspension of the desired feed or ingredient in a water or oil phase to the pellets under reduced pressure and subsequently increasing the pressure. The method results in pellets with a high degree of loading and in which the active ingredients are homogeneously distributed.

FIELD OF THE INVENTION

The present invention relates to a method for preparing feed pellets.The process for the addition of sensitive ingredients during thepreparation of pellets is so altered that activity losses are minimized.Specifically, the pellets are treated by mixing a suspension or solutionof active ingredients in a fluid phase (for example oil or water) underappropriate conditions with carrier material which has been previouslygranulated.

BACKGROUND OF THE INVENTION

Feed is generally prepared by mixing different ingredients which arefound to be necessary (active ingredients) with carrier materialsessential to obtain the feed in the desired form. The desired form maybe a powder, a pellet, a solution or a suspension. The preferred formwill depend on the application conditions, the composition and thetransport.

A well known problem in feed preparation is the loss of active substanceduring the pelleting process, especially when extrusion is used.Extensive research results have been published describing the loss ofactivity of the active ingredients during extrusion cooking.

Lee et al. (AIChE Symposium Series (1978) 172: 192-195) investigated thestability of vitamin A in extrusion cooking processing. The percent ofretention of the different tested forms of vitamin A ranged from 50 to100%. This was reported to be relatively stable when compared with theretention of cantaxanthin which was reported to be in the range of 30 to35%. Berset (Ind. Aliment. Agric. (1987) 104: 529-533) reports a loss of18% of cantaxanthin when a commercial preparation was treated. Henckenand Estermann (Aquaculture Ind. Develop. Report (1991) 91: 34-51) reporta 25 to 48% loss of activity of synthetic astaxanthin during fish feedpreparation using extrusion cooking.

A possible solution to this loss of active substance during granulationis to add the active ingredient in a suitable form like a suspension orsolution in a fluid phase subsequent to the granulation step. Mixing ofcomponents with a fluid phase can be difficult since active ingredientsare not always soluble. Furthermore, the addition after the extrusionstep makes it more difficult to obtain a homogenous product.

High concentrations of active ingredients in feed for cattle, poultry orfish in a form which is easy to handle and easy to quantify can beobtained by soaking granulated particles with a suspension or solutioncontaining the desired feed or ingredients thereof. The granulatedmaterial contains pores which are filled with the solution or suspensionand the loaded pellets can easily be used.

The loading of the pellets is generally performed at atmosphericpressure. The process poses some severe drawbacks:

it is difficult to reproduce the amount of suspension or solution whichis absorbed into .the pellets, this is especially relevant if the aim isto control the amount of fluid (oil etc.) which is fed to the animalconcerned,

the pellets are generally preferentially covered at their surface, whichmay cause problems (like oxidation) of the active ingredient,

the particles in the suspension may block the pores leading to aninefficient use of the particle pore volume and to the above mentionedsurface phenomena.

There is thus a lack of reproducibility in dosage of the activesubstance and a higher chance to losses of active ingredient as aconsequence of insufficient penetration of the active ingredient in thefeed granule.

To avoid these problems granulated material with wide pores can be usedbut this evidently leads to loss of strength of the loaded pellets.

The present invention overcomes the problems described above.

SUMMARY OF THE INVENTION

The present invention discloses a method for minimizing the loss ofactivity of sensitive materials due to the well known extrusion process.The invention discloses that this can be done by addition of thematerial after the extrusion process. The invention is exemplified bythe addition of astaxanthin in oil to feed pellets. The invention thusdiscloses a method for preparing feed pellets loaded with an activeingredient comprising the addition of active material after theextrusion process. The active ingredient is an enzyme, a vitamin, apigment or a carotenoid. Preferably, the active ingredient isastaxanthin.

The present invention further provides a method for preparing pelletswhich are homogenously loaded with active ingredient. In one embodiment,the method comprises the addition of a suspension or solution of theactive ingredients to pellets optionally under reduced pressure, soakingunder reduced pressure and subsequently increasing the pressure.Preferably, the addition is performed under vacuum.

The present invention also provides feed pellets which have beenobtained by this method. Specifically, fish meal pellets soaked with anoil suspension containing astaxanthin are disclosed. Such pellets can berecognized by their high degree of loading which is moreover relativelyhomogenous. A fish pellet is disclosed which contains more than 81.5 mgastaxanthin per kg dry matter.

DETAILED DESCRIPTION OF THE FIGURES

FIGS. 1(A)-1(C) shows the spraydried Phaffia rhodozyma suspended in oilafter one (A), two (B) and three (C) passes through a bead mill.

FIGS. 2(A)-2(C) shows the results of the addition of the suspensions ofFIGS. 1 (A), (B) and (C) under atmospheric pressure to the fish mealpellets.

FIGS. 3(A)-3(C) shows the results of the addition of the suspensions ofFIGS. 1 (A), (B) and (C) under vacuum to the fish meal pellets.

DETAILED DESCRIPTION OF THE INVENTION

The present invention discloses a method for preparing feed pellets. Thepresent invention discloses how the loss of activity of sensitivematerials due to the well known extrusion process can be minimized. Theinvention discloses a a method for preparing feed pellets loaded with anactive ingredient comprising the addition of active material after theextrusion process. The extrusion process can also be the so-calledextrusion cooking process. The active ingredient is an enzyme orprotein, a pigment or a carotenoid.

The addition of the active ingredient (or any ingredient which can bedamaged by the extrusion process) after the extrusion process may causea problem due to the fact that the extrusion process also serves toobtain a homogenous feed pellet. This problem can be circumvented by theaddition of a suspension or solution of feed or ingredients thereof in afluid phase to the pellets optionally under reduced pressure, soakingunder reduced pressure and subsequently increasing the pressure. Thereduced pressure can be vacuum.

The fluid phase can be any fluid (for example water or oil) providedthat the active ingredient can be dispersed or dissolved in this fluid.In the present examples capelin-oil is used.

The present invention discloses a method for preparing pellets loaded ina controlled manner with active ingredients. The method comprises theaddition under mixing of a suspension or solution of feed or ingredientsthereof in a fluid phase to the pellets, soaking under vacuum andsubsequently releasing the vacuum.

The pellets are composed of an edible material. The specific compositiondepends on the desired characteristics of the material. The choice ofthe pellet, volume, weight and pore diameter also depends on the kind offeed one wants to use and on the application for which the loadedpellets are meant. A preferred pellet material in the present inventionis fish meal.

The feed or feed ingredient may be any ingredient that is needed. Thechoice may depend on the nutritional value or on certain theologicalcharacteristics which may be obtained by the activity of the ingredient.In the following some examples of feed or feed ingredients will bediscussed. In general terms enzymes or proteins, pigments, vitamins,antioxidants, colouring agents and carotenoids can be employed.Obviously combinations of these ingredients can be added, simultaneouslyor successively.

a) Enzymes

In general all feed enzymes can be used in the present method and theseinclude phytase, amylase and protease. Amylase may be brought on thepellet and subsequently the pellets can be mixed with feed. It is alsopossible to add the enzyme suspension after pelletizing/extrusion. Theactivity of this enzyme can be quantified and the added amountcontrolled. The enzyme can change the fluidity of the feed to which itis added or improve the digestability of feed components. Anotherexample of an enzyme is phytase here again the dosage can be controlledby the method of the present invention.

b) Carotenoids

Astaxanthin is used as a natural colourant for salmonids. Astaxanthincannot be solubilized in a water phase. A suspension of astaxanthin inoil or a suspension of Phaffia rhodozyma cells (or cell fragments)containing astaxanthin in oil, can be used to soak the pellets.Incidentally, it was found that this astaxanthin contrary to thecommercial synthetic astaxanthin as used by Hencken and Estermann (1991,opt. cit.) could form a stable suspension in oil.

The amount of oil and astaxanthin fed to the fish can thus becontrolled. The control of the amount of oil provides a way ofinfluencing the growth rate of the fish.

Other carotenoids which can advantageously be used in the method of thepresent invention include β-carotene, cantaxanthin and zeaxanthin.

Desired pellets are brought under vacuum and the liquid phase which maybe a solution or suspension of desired feed or ingredients thereof orother ingredients in a water or oily phase is added under reduced oratmospheric pressure. The equipment used can range from a waterjet and aflask which can be vacuated at laboratory scale via a Rotorvapor tolarge scale equipment.

The pellets obtained by the present method show a high degree ofloading, moreover the pellets are loaded relatively homogenously.Furthermore, the amount of loading can be regulated by regulating theamount of fluid phase added. This is especially important if one wantsto regulate the amount of oil provided to the desired animal, e.g.,fish.

The present invention discloses, for example, fish meal pellets whichcontain more than 30 mg and preferably more than 81.5 mg astaxanthin perkg of dry matter.

The present invention thus provides a method for preparing feed pelletswherein the active ingredient is added after the extrusion. The feedpellets are subsequently loaded under reduced pressure which makespossible an acurate, reproducible and homogenous loading.

EXAMPLE I Preparation of an Oil Suspension Containing Astaxanthin

A Phaffia rhodozyma culture was centrifuged and dried by spraydrying.The spraydried powder (dp_(p) =100 μm) was suspended in a commercialfish-oil (Capelin oil). The mixture of cell material containingastaxanthin and oil was ground in a bead mill. After one pass of millingthe particle diameter was determined. Microscopic analysis indicatedthat a large proportion of the spraydried powder particles weredisintegrated. A small portion of the particles (<5%) was unaffected andhad a diameter of about 100 μm (FIG. 1A). The astaxanthin concentrationwas about 630 ppm (Suspension I).

A second suspension was prepared (Suspension II) by grinding theparticles three times in a bead mill (FIG. 1C). Microscopic analysisrevealed that practically all cells were disintegrated, the largestagglomerates of cells had a diameter of less than 20 μm.

The astaxanthin concentration was 330 ppm.

EXAMPLE II Soaking of Fish Meal Pellets

Commercial fish meal pellets were obtained from Trouw International(Putten, the Netherlands). These pellets were semi-manufactured, whichmeans that they had not been treated with oil. These pellets have adiameter of 8 mm, a length of between 0.8 and 1.2 mm and a weight ofbetween 220 and 330 mg.

Further experiments have all been performed in duplicate, data reportedare the mean values.

A. Soaking at atmospheric pressure

100 g of fish meal pellets were brought into a i L beaker. 25 g of anoil suspension containing about 8 mg astaxanthin, was added (SuspensionII or twice diluted Suspension I). Mixing was performed during 1 hour ina Turbula mixer.

B. Soaking under vacuum

100 g fish meal pellets were dried under vacuum for 30 min. at 60° C. ina 500 ml flask in a Rotorvapor. Vacuum was obtained using a waterjet. 25g of an oil suspension containing astaxanthin was added (as above) insmall amounts with vacuum application in between. Rotation was continuedfor 10 min. and the flask was subsequently cooled on an ice bath.

EXAMPLE III Analysis of Soaked Pellets

A. Microscopic analysis

When pellets were prepared at atmospheric pressure the pellets obtainedusing Suspension I mainly gave a red colour (astaxanthin) at the surface(FIG. 2A). Pellets obtained using Suspension II showed a red colour alsoin the interior but the concentration at the surface was higher (FIG. 2Band C).

When pellets were prepared under vacuum according to Example II.B.,Suspension I gave pellets with red colour in the interior and Phaffiamainly at their surface (FIG. 3A). With Suspension II the red colour wasmainly in the interior of the pellet (FIGS. 3B and C).

Reduction of particle size and application of the Suspension undervacuum clearly gives a better reproducible result.

B. Washing test

The release of astaxanthin from the particles was simulated by washingthe pellets. The amount of astaxanthin was determined using HPLC.

Experiments were performed as follows.

a) 50 g fish meal pellet was brought in a 250 ml flask,

b) 100 ml water of 10° C. was added,

c) the flask was put in a Shake Water Bath at 10° C., 75 strokes permin. 4.5 cm amplitude for 5 min.

d) after shaking the particles were immediately sieved over a sieve withholes of 1 mm diameter,

e) the astaxanthin concentration was determined in untreated pellets,washing water and in the washed pellets, using HPLC.

The following amounts of astaxanthin were found.

A. Atmospheric pressure

                  TABLE I                                                         ______________________________________                                                                      asta mg/kg                                      Suspension I                                                                            dry matter                                                                             asta mg/kg dry matter                                                                           asta loss                                ______________________________________                                        Pellets   0.94     73.0       77.6                                            Washwater          1.3        1.5    1.9%                                     Washed pellets                                                                          0.83     66.0       79.5                                            ______________________________________                                    

                  TABLE II                                                        ______________________________________                                                                      asta mg/kg                                      Suspension II                                                                           dry matter                                                                             asta mg/kg dry matter                                                                           asta loss                                ______________________________________                                        Pellets   0.95     74.8       78.7                                            Washwater          0.28       0.4    0.5%                                     Washed pellets                                                                          0.82     66.9       81.5                                            ______________________________________                                    

B. Under vacuum

                  TABLE III                                                       ______________________________________                                                                      asta mg/kg                                      Suspension I                                                                            dry matter                                                                             asta mg/kg dry matter                                                                           asta loss                                ______________________________________                                        Pellets   0.94     82.0       86.3                                            Washwater          1.5        1.6    1.8%                                     Washed pellets                                                                          0.86     73.0       84.8                                            ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                                                      asta mg/kg                                      Suspension II                                                                           dry matter                                                                             asta mg/kg dry matter                                                                           asta loss                                ______________________________________                                        Pellets   0.95     82.4       86.7                                            Washwater          0.16       0.2    0.2%                                     Washed pellets                                                                          0.75     64.2       85.6                                            ______________________________________                                    

It is clear that the loss of astaxanthin is lower when particle diameteris smaller (Suspension II). And that the loss is further reducedconsiderably when pellets are treated with active ingredients that areabsorbed under vacuum.

The above examples merely serve to illustrate the principle underlyingthe invention and in no way are meant to determine the scope of thedisclosure.

We claim:
 1. A method for loading feed pellets with an active ingredient, comprising the steps of:(a) adding to dried pellets the active ingredient in a fluid phase, wherein said active ingredient is particulate material which has been ground such that essentially all the material is disintegrated and remaining particles have an average diameter of less than about 20 μm; (b) allowing the pellets to soak in said fluid containing said active ingredient under reduced pressure; and (c) subsequently increasing the pressure, thereby loading the active ingredient into the pellets.
 2. A method for loading feed pellets with an active ingredient distributed substantially homogeneously throughout the pellets, comprising the steps of:(a) adding to dried pellets the active ingredient in a fluid phase, wherein said active ingredient is particulate material which has been ground such that essentially all the material is disintegrated and remaining particles have an average diameter of less than about 20 μm; (b) allowing the pellets to soak in said fluid containing said active ingredient under reduced pressure; and (c) subsequently increasing the pressure, thereby loading the active ingredient distributed substantially homogeneously throughout the pellets.
 3. The method of claim 2 wherein the active ingredient is an enzyme, a pigment, a protein, a vitamin or a carotenoid.
 4. The method of claim 2 wherein said reduced pressure is produced by applying a vacuum.
 5. The method of claim 2 wherein the fluid phase is oil.
 6. The method of claim 3 wherein the active ingredient is an enzyme selected from the group consisting of phytase, lactase, protease and amylase.
 7. The method of claim 3 wherein the active ingredient is a carotenoid selected from the group consisting of astaxanthin, β-carotene, cantaxanthin and zeaxanthin.
 8. The method of claim 2 wherein the sequence of steps (a), (b) and (c) is repeated at least one time.
 9. A method for preparing feed pellets loaded with an active ingredient, comprising:(a) drying said pellets; (b) adding to said dried pellets the active ingredient in a fluid phase, wherein said active ingredient is particulate material which has been ground such that essentially all the material is disintegrated and remaining particles have an average diameter of less than about 20 μm; (c) allowing the pellets to soak in said fluid containing said active ingredient under reduced pressure; and (d) subsequently increasing the pressure, thereby loading the active ingredient distributed substantially homogeneously throughout the pellets.
 10. A method for preparing extruded feed pellets loaded with an active ingredient comprising:(a) extruding pellets; (b) drying said pellets; (c) adding to said dried pellets the active ingredient in a fluid phase, wherein said active ingredient is particulate material which has been ground such that essentially all the material is disintegrated and remaining particles have an average diameter of less than about 20 μm; (d) allowing the pellets to soak in said fluid containing said active ingredient under reduced pressure; and (e) subsequently increasing the pressure, thereby loading the active ingredient distributed substantially homogeneously throughout the pellets.
 11. A feed pellet containing at least about 30 grams of astaxanthin per kilogram of dry matter, which astaxanthin is distributed substantially homogeneously throughout the pellet.
 12. A feed pellet according to claim 11 which contains at least about 77 grams of astaxanthin per kilogram of dry matter.
 13. A feed pellet according to claim 11, produced by loading dried pellets with astaxanthin from dried ground Phaffia rhodozyma cells which have been ground such that essentially all the material is disintegrated and any particles remaining after grinding have an average diameter of less than about 20 μm. 